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Growth hormone axis · Metabolic & endocrine

IGF-1 LR3

A modified long-acting IGF-1 analogue sold for bodybuilding, and not the same thing as approved IGF-1 medicine.

L1Theory onlyNot approved for this useUnclear
How settled this rating is:
very-low confidence in the current evidence rating
Routes studied:
Not established · Subcutaneous injection, Intramuscular (marketed but never approved)
Also known as:
long R3 IGF-1, IGF-1 Long R3
Last reviewed:
2026-09-06
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Evidence passport

Last reviewed 2026-09-06

A one-screen summary of what is known about this compound. Every field describes the evidence and legal status — not how safe or effective it is, and not a recommendation. The 0-100 figures are evidence-strength ratings, not percentages.

Evidence level (type of study, not a quality rating)
L1Theory only
How settled this rating is
Very low confidence in rating
Human efficacy evidence
5 of 100 evidence strength
Human safety evidence
8 of 100 evidence strength
Regulatory status
Not approved for this use
Development
Unclear
Routes
SC injection· unapprovedIM· unapproved
Evidence base
Mostly animal and lab studies
Furthest stage
Not established
Source curation
Sources fully curated
How far human research has progressed
No adequate human trial evidence for the LR3 analogue itself

Most of this evidence comes from animals and cells

The supporting research for IGF-1 LR3 is predominantly preclinical (Level 1–2). That is a legitimate starting point for science and a poor basis for personal decisions. Human results are not simply a scaled-up version of mouse results.

Overview

Human efficacy evidence strength5 of 100 evidence strength

Higher = more and better-quality human evidence. It does not mean the effect is bigger or that the compound works for you.

Preclinical (animal / lab) evidence strength40 of 100 evidence strength

Higher = more animal, tissue or cell research. Preclinical results are a starting point, not proof of a human benefit.

Human safety evidence strength8 of 100 evidence strength

Higher = more mature, better-documented human safety data. It does not mean the compound is safer than one with a lower number.

How to read these scores

Every number here rates the evidence, not the compound. They are editorial 0-100 strength ratings, not percentages, and not a rating out of five stars.

  • Human efficacy evidence strength — Higher = more and better-quality human evidence. It does not mean the effect is bigger or that the compound works for you.
  • Preclinical evidence strength — Higher = more animal, tissue or cell research. Preclinical results are a starting point, not proof of a human benefit.
  • Human safety evidence strength — Higher = more mature, better-documented human safety data. It does not mean the compound is safer than one with a lower number. A score of 80 does not mean “80% safe”.
  • Evidence level (L0-L5) — the strongest type of study behind the compound, from anecdote (L0) to large replicated human trials (L5). It is a description of the study evidence, not a quality, safety or recommendation rating.
  • Confidence — how likely we think it is that this rating changes as new research lands. Low confidence means the picture is unsettled, not that the compound is bad.

None of these ratings is medical advice, a safety guarantee, or a recommendation to use anything. How we grade evidence.

How far human research has progressed: No adequate human trial evidence for the LR3 analogue itself

Routes & formulations

Marketed / research routes — never approved

SC injection· unapprovedIM· unapproved

Marketed for injection. Approved IGF-1 therapy exists as a supervised medicine for defined rare conditions; that approval provides no support for research-market LR3 products.

Route availability is not evidence of efficacy, and evidence from one route does not transfer to another. The Registry never provides dosing or sourcing information.

Peptide lifecycle

  1. Discovery

  2. Preclinical

  3. Phase I

  4. Phase II

  5. Phase III

  6. Approved

UnclearFurthest stage not established in our curated record

There is no pharmaceutical development programme for IGF-1 LR3 in our record. It exists primarily as a laboratory reagent and research-market product.

What it is

A modified version of IGF-1 with an extended N-terminal sequence and an amino-acid substitution that reduce binding to IGF binding proteins, giving a longer-acting molecule originally made for cell-culture research.

What people claim

  • Muscle growth and hyperplasia
  • Nutrient partitioning and fat loss
  • Enhanced recovery between training sessions

What the evidence actually says

Primary human evidence for LR3 specifically is thin to the point of absence — we say that plainly rather than borrowing credibility from approved IGF-1 medicine. What exists is IGF-1 receptor biology, cell-culture data, and a large volume of community reporting. The relevant risks here are twofold: an unresolved growth-signalling question and a completely unregulated supply chain.

Related evidence

Useful next reads based on this compound — not recommendations.

Human evidence

  • No adequate controlled human trial of IGF-1 LR3 for muscle, performance or body-composition outcomes was identified in our curated record.
  • A 2026 peer-reviewed review documents IGF-1 LR3 among substances self-administered outside medical supervision — a use pattern, not an efficacy finding.
  • Approved recombinant IGF-1 evidence applies to a different product and different patient populations.

Preclinical evidence

  • Cell-culture and animal work on IGF-1 receptor signalling, protein synthesis and satellite-cell proliferation.

Animal and cell findings are Level 1–2 evidence.

Mechanism and pathways

  • IGF-1 receptor agonism drives anabolic signalling pathways in muscle and other tissues.
  • Reduced binding-protein interaction increases free activity — which also removes a natural regulatory brake.

Safety and unknowns

  • Hypoglycaemia is a recognised hazard of IGF-1 pathway activity and is described in approved IGF-1 labelling.
  • No human safety dataset exists for LR3 products, and content and purity of unregulated material are unverifiable.

Cancer relevance

This section covers questions raised by how the compound works in the body, plus anything regulators and trial teams keep an eye on. It is not a statement that this compound causes cancer — for most compounds here, no human data exist in either direction.

Theoretical / mechanistic concern only

Sustained IGF-1 receptor signalling is one of the better-grounded theoretical cancer concerns in this field, given its role in cell proliferation. That is a mechanistic concern, not a demonstrated human risk for this product — and the absence of studies is not reassurance.

Regulatory status

Not an approved medicine in any region. It must not be confused with approved recombinant human IGF-1 (mecasermin), which is licensed for specific rare growth disorders under medical supervision and is a different product with a different evidence base. IGF-1 LR3 is prohibited in sport.

Evidence grade

L1Theory onlyVery low confidence in rating

Cell, receptor or computer work explaining how something could work in principle. No evidence yet that it does anything useful in people.

What would change our rating?

  • Controlled human data on the LR3 analogue itself.
  • Any regulated safety or pharmacokinetic dataset.

References and sources

Sources fully curated

Source hierarchy: regulatory documents and trial registries first, peer-reviewed work next, sponsor material flagged as non-independent. We never use supplier or clinic marketing as evidence, and where a verified source has not yet been curated we say so rather than inventing one.

Evidence change history

These entries record changes to our assessment of the published evidence — not changes to the compound itself.

No recorded changes yet. Baseline position set on 2026-09-06.